Software systems employing graphical user interfaces are virtually standard in modem computer operating systems. Key to the acceptance of a graphical user interface in new environments, such as on the flight deck of an airplane, are devices that allow a user to control the position of a cursor on the computer system display.
For some time, the cursor control device of choice for use with a graphical user interface has been the "mouse." In the most common mouse cursor control device, a ball is mounted in a housing so that part of the ball projects from the housing when the mouse is in its normal position of use. A user causes the ball to rotate relative to the housing by placing the projecting part of the ball against a surface, and dragging the device across the surface, so that the ball rotates due to the friction of the ball against the surface. The rotation of the ball controls an electrical signal that in turn controls the location of a cursor on a computer-controlled display.
The second most preferred type of cursor control device for use with a graphical user interface is probably the trackball. A trackball cursor control device corresponds to a mouse rotated vertically 180 degrees, or turned over, so that the user acts directly upon the ball to cause its rotation, rather than dragging the device across a surface. As there is no need to drag the trackball across a surface, typically the position of the housing for the trackball is fixed relative to the user.
While the foregoing cursor control devices are the preferred types, these devices have disadvantages when used on moving vehicles, such as aircraft. The principal problem is that loose components, such as a mouse, are undesirable on moving vehicles, because the components may move relative to the interior of the vehicle during accelerations of the vehicle, creating a hazard, and resulting in undesired cursor movement. This problem also arises with trackball cursor control devices, since acceleration of the vehicle can cause the trackball to rotate, particularly if a user's hand idly rests on the ball during changes in the speed or direction of the vehicle.
One proposed solution to the foregoing problem is to provide a touch sensitive display in moving vehicles. Cursor control is provided by the user touching the screen of the display with a finger. Touch-controlled displays (or overlays that provide the same function) have the advantage that there are no parts that can move independent of the user and cause undesired cursor movement.
Unfortunately, touch sensitive displays have four principal disadvantages.
First, the touch sensitive screen or overlay rapidly becomes obscured by fingerprints, and thus, so does the underlying display. Second, touch sensitive overlays are dedicated to one display. It is not possible to use a single touch sensitive overlay to control multiple displays. Third, touch sensitive displays or overlays operate in an "absolute" mode. Finger pressure on a touch sensitive screen causes the cursor to be moved to the display position lying beneath the location of the finger. In contrast, mouse and trackball cursor control devices operate in relative mode. The distance and direction a trackball rotates relative to a previous position is used to control the location of the cursor. While touch sensitive screens allow a cursor to be rapidly moved to a desired location, they are relatively imprecise due to the size of a user's finger. In contrast, a mouse or trackball is relatively precise because much smaller cursor movements can be accommodated. Fourth, vehicle acceleration can cause a user's fingers to move inadvertently when using a touch sensitive screen resulting in the cursor being moved to an undesired location.
The present invention provides a touch-pad cursor control device that provides a solution to the problems with prior art cursor control devices of the type described above.